Many modern devices require hermetic environments to operate and many amongst these are “active” devices which require electrical biasing. Displays such as organic light emitting diodes (OLED) that require light transparency and biasing are demanding applications due to their need for absolute hermeticity as a result of the use of electron-injection materials. These materials would generally decompose at atmosphere within seconds otherwise, so the respective device should maintain vacuum or inert atmospheres for long periods of time. Furthermore, the hermetic sealing should be performed near ambient temperatures due to high temperature sensitivity of the organic material to be encapsulated.
Frit-based sealants, for instance, include glass materials ground to a particle size ranging typically from about 2 to 150 microns. For frit-sealing applications, the glass frit material is typically mixed with a negative CTE material having a similar particle size, and the resulting mixture is blended into a paste using an organic solvent or binder. Exemplary negative CTE inorganic fillers include cordierite particles (e.g. Mg2Al3[AlSi5O18]), barium silicates, β-eucryptite, zirconium vanadate (ZrV2O7), or zirconium tungstate, (ZrW2O8) and are added to the glass frit, forming a paste, to lower the mismatch of thermal expansion coefficients between substrates and the glass frit. The solvents are used to adjust the rheological viscosity of the combined powders and organic binder paste and must be suitable for controlled dispensing purposes. To join two substrates, a glass frit layer can be applied to sealing surfaces on one or both of the substrates by spin-coating or screen printing. The frit-coated substrate(s) are initially subjected to an organic burn-out step at relatively low temperature (e.g., 250° C. for 30 minutes) to remove the organic vehicle. Two substrates to be joined are then assembled/mated along respective sealing surfaces and the pair is placed in a wafer bonder. A thermo-compressive cycle is executed under well-defined temperature and pressure whereby the glass frit is melted to form a compact glass seal. Glass frit materials, with the exception of certain lead-containing compositions, typically have a glass transition temperature greater than 450° C. and thus require processing at elevated temperatures to form the barrier layer. Such a high-temperature sealing process can be detrimental to temperature-sensitive workpieces. Further, the negative CTE inorganic fillers, which are used in order to lower the thermal expansion coefficient mismatch between typical substrates and the glass frit, will be incorporated into the bonding joint and result in a frit-based barrier layer that is substantially opaque. Based on the foregoing, it would be desirable to form glass-to-glass, glass-to-metal, glass-to-ceramic, and other seals at low temperatures that are transparent and hermetic.
While conventional laser welding of glass substrates can employ ultra-high laser power devices, this operation at near laser ablation often times damages the glass substrates and achieves a poor quality hermetic seal. Again, such conventional methods increase the opacity of the resulting device and also provide a low quality seal.
In some instances, the seal may not be optically clear, e.g., may be colored. These deficiencies are particularly detrimental in the case of sealed packages used for emitting, transmitting, converting, extracting, diffusing, and/or scattering light. For example, opaque seals may block light transmission, whereas seals that are not optically clear may undesirably distort light as it passes through the sealed region. For these reasons, sealants are often applied around the perimeter of a substrate, e.g., in a frame around an item to be sealed or only at the edges even if no item is sealed in the package. Nonetheless, the material at the edges can still undesirably distort or reduce light transmission in some configurations.
Accordingly, it would be advantageous to provide methods for laser sealing substrates, which may, among other advantages, increase seal transparency, strength, and/or hermeticity, decrease manufacturing cost and/or complexity, and/or increase production rate and/or yield. It would also be advantageous to provide sealed devices for displays and other electronic devices which can have improved light transmission and/or decreased distortion. The resulting sealed devices can themselves be used as components in display or other electronic devices or can be used to protect a wide array of electronics and other components, such as light emitting structures or color converting elements, e.g., laser diodes (LDs), LEDs, OLEDs, and/or QDs.